adds a journaled_class method

That way we do not have to load the class or do some magic parsing names when wanting to now what is journaled.

vendor/plugins/acts_as_journalized/lib/acts_as_journalized.rb

@@ -115,6 +115,9 @@ module Redmine
               c.class_eval("belongs_to :journaled, :class_name => '#{name}' #{include_option}")
               c.class_eval("belongs_to :#{name.gsub("::", "_").underscore},
                   :foreign_key => 'journaled_id' #{include_option}")
+              c.class_eval("def self.journaled_class
+                              #{self}
+                            end")
             end
           end
         end